(a) Field of the Invention
The present invention relates to an optical recording device having a defect detection system and, more particularly, to a technique for detecting a defect generated in a groove pattern or in a recorded/reproduced data and the cause of the defect during the operation of the optical recording device.
(b) Description of the Related Art
Exposure of an optical disk to form a groove pattern on an optical disk or recording/reproducing operation of an optical disk is generally performed by an optical recording device having a laser source. In the exposure or recording/reproducing operation by using a laser beam, the focal position of the beam spot and a laser power from a laser source should be fixed without fluctuation in order to form a stable pattern in the exposure, to record an accurate data in the recording operation or reproduce an accurate data in the reproduction.
However, a fluctuation of the focal position or laser power is sometimes observed in the optical recording device after a continuous long time operation because of the change of the characteristics in the constituent elements or unstable factors of the optical recording device, and causes a defect in the exposure or recording/reproducing operation. If a defect is found in the resultant groove pattern or in the recorded data, the cause of the defect is generally examined in the optical recording device after the exposure or recording/reproducing operation is finished, because the examination and the operation cannot be performed concurrently.
The fluctuation of the focal position enlarges the diameter of the beam spot on the optical disk, which reduces the effective laser energy per unit area for the resultant groove pattern or in the recorded mark. As a result, an effective exposure or recording/reproducing operation can be achieved only in the central part of the beam spot which has a higher power density compared to the peripheral area of the beam spot. Accordingly, the size of a resultant groove pattern or recorded mark becomes smaller in the case of fluctuation of the focal position compared to the case of a normal focal position, and degrades the quality of the groove pattern, recorded data or reproduced data.
The defects caused by the fluctuation of the focal point and by the fluctuation of the laser power are similar so that it is generally difficult to determine the cause of the defect by examining the recorded mark or reproduced data during the exposure or recording operation, i.e., whether the defect is due to the fluctuation of the focal position or laser power from the laser source. The determination of the cause takes a long time examination, which reduces the throughput of the exposure or recording/reproducing.